A sucker rod pump assembly includes a pump located in the production tubing of an oil producing well below the level of the liquid in the well. The pump is operated by a string of reciprocating sucker rods that extend through the production tubing from the pump to the surface. The rods are reciprocated by a pump jack located at the surface. When the fluid being pumped reaches the surface, it is directed into a lateral flow line by a stuffing box mounted on the wellhead. The stuffing box has an opening through which the top sucker rod extends. Seals located in the stuffing box allow the sucker rods to reciprocate in the opening while preventing the pumped fluid from flowing through the opening. The top sucker rod is usually a special rod, called a "polish rod", with an outer surface that is machined to a very smooth finish to reduce the friction between the rod and the seals in the stuffing box.
The friction generated by the reciprocation of the polish rod, however well machined, through the seals produces heat. This heat contributes to the deterioration of the seals and the polish rod. The improved stuffing box of the present invention lubricates and at the same time cools the polish rod as it moves through the stuffing box in a manner requiring low maintenance, thereby increasing the life of the rod and packing at low cost.
Various prior art devices have attempted to align, cool or lubricate the stuffing box.
Stogner (U.S. Pat. No. 3,474,734) and Haentjens (U.S. Pat. No. 3,516,759) both provide for lubricating a stuffing box by means of reservoirs mounted separately from the housing of the stuffing box. Stogner teaches a stuffing box for a rotary pump, Haentjens for a centrifugal pump. In both schemes, lubricant is delivered to the interior of the stuffing box by means of a pressure delivery system. Neither Stogner nor Haentjens teach a system that allows the lubricant to freely circulate from the interior of the housing to the reservoir and back again. Neither system teaches cooling as well as lubricating. Both systems depend upon one-way valves and pressure to direct the passage of the lubricant to the chamber and to keep it there.
Orr (U.S. Pat. No. 3,209,630) discloses a stuffing box for mounting on the upper end of oil well tubing where a polish rod reciprocating through an "extension tube" section of the stuffing box is bathed in lubricating fluid supplied from an exterior reservoir mounted near the stuffing box. Orr does not provide for changing the lubricating fluid as it becomes heated and thus does not provide for cooling.
Reeves (U.S. Pat. No. 3,468,374) provides for cooling and lubricating a polish rod as it reciprocates in a stuffing box, however, Reeves does not use a lubricating fluid reservoir. Reeves uses the production fluid itself as the lubricating fluid and uses the high pressure in the production tubing to cause the lubricating fluid to flow into and out of the cooling and lubricating chamber. Appropriate one-way valves are provided. In the absence of high pressure production fluid, Reeves provides for only a static reserve of fluid that lubricates but does not circulate into and out of the lubricating chamber and thus does not cool the lubricating oil. Moreover, Reeve's scheme cannot cool below the temperature of the production fluid itself, which may be hot.
It is an object and feature of the present invention to provide a stuffing box for a sucker rod pump assembly wherein cooled lubricating fluid displaces continuously the heated lubricating fluid adjacent the polish rod by the convection currents produced by the heating of the lubricating fluid adjacent the polish rod and the cooling of the lubricating fluid away from the polish rod.
It is another object of this invention to provide a stuffing box having a tubular housing through which a polish rod may reciprocate with seals located in the housing that are spaced longitudinally to provide an annular chamber for lubricating fluid to surround the polish rod and a lubricating fluid reservoir from which cool lubricating fluid will flow into the bottom of the chamber and displace, by convection, lubricating fluid, warmed by the heat in the polish rod, from the top of the chamber back to the reservoir to be cooled.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification including the attached drawing and appended claims.